1. Field of The Invention
The present invention relates generally to pressure vessels for pressurized secondary cells and, more particularly, to metal gas cells such as nickel hydrogen aerospace secondary storage cells. Specifically, the present invention relates to an improved secondary storage battery made from secondary cells having improved pressure vessels for such cells.
2. Description of the Prior Art
Metal gas cells, and in particular nickel hydrogen batteries, have generally included an elongated plate stack encased within a sealed metal vessel. The vessel is generally in the form of a single cylindrical vessel having dome-shaped ends and charged with a gas under pressure, such as hydrogen. Such single cells have represented an entire battery in order to restrict the need for manufacturing more than one pressurized vessel casing. An example of such secondary cells useful as aerospace batteries is disclosed in U.S. Pat. No. 4,950,564, the contents of which are hereby specifically incorporated herein by reference.
As can be seen from the referenced patent, a plurality of stacked plates are mounted together within the single containment vessel. While this particular design has provided a secondary cell and battery which is quite effective, there are certain drawbacks to this type of structure in general. In existing designs, electrodeplates are circular in form to conform to the cylindrical enclosure. Unfortunately, the use of such circular shaped electrodes results in substantial scrap material when blanked out from larger rectangular materials. Moreover, the present design requires a multiplicity of smaller diameter positive electrodes utilizing multiple belleville washers to maintain proper stack compression for the expected long life. This complicated design, unfortunately, adds weight to the cell, and weight in aerospace applications is a critical factor. In addition, circular electrode plates require elongated plate tabs and electrical leads to connect the plates to their respective terminal connectors within the containment vessel. This again leads to complexity and weight for the cell. Therefore, there remains a need to provide a secondary cell and battery structure having the output requirements of existing designs yet having simpler construction and lighter weight, thereby enhancing the energy density capability as well as reducing the possible failure points.